Neutron activitation is a valuable methodology to determine the identity of materials having a characteristic elemental composition. For example explosives can be characterized and by their unique ratios of Carbon, Ozygen and Nitrogen. Many neutron activitation applications, including identification for explosives relies on the emission of high energy gamma rays. In real situations with shielding material surrounding material the high energy gamma rays are more likely to emerge for possible detection than low energy gamma rays. Unfortunately these same high energy gamma rays are hard to detect with full energy deposition making collection of the energy spectra inefficient. A neutron activation and detection system is desired that can both identify and locate a shielded source of unknown type and quantity using only a few detected gamma rays.
The identification of the illicit movement of suspect materials requires a system capable of identifying the material and locating the source. Innocuous monitoring of movement in open staging or storage areas is highly desirable but difficult to achieve. Conventional neutron activation monitoring techniques involve illumination of the suspect area with neutrons and subsequent detection of emitted characteristic radiation, the identification of the energy of those emitted radiations and correlation of the measured energy or energies to the known emissions spectra of isotopes. Gamma ray spectra are useful for identifying an isotope, but not for locating it. Various imaging techniques can be used in conjunction with the energy spectroscopy including physical collimation of the incident neutrons or directional information of the emitted gamma-ray radiation by collimation, coded aperture arrays or conventional Compton cameras. Current methods for locating material by neutron activation typically rely on collimators and require long data acquisition times when the location of the material is not know.